1. Field of the Invention
The present invention relates to an automatic vehicle driving system and a method of driving the same, and more specifically to a system and a method of driving a test vehicle placed on a chassis dynamometer via an accelerator actuator. Here chassis dynamometer is used to measure engine power of a test vehicle whose front or rear driving wheels are placed on two opposing rollers, in order to realize the same conditions as at the outdoor driving test. In this specification, "accelerator" is referred to as "accel" simply, hereinafter.
2. Description of the Prior Art
The chassis dynamometer is used to measure exhaust gas components, fuel consumption rate, etc. of a test vehicle placed on the chassis dynamometer rollers. Therefore, it is preferable to drive the test vehicle by an automatic vehicle driving system provided with air cylinders small in size, light in weight, and easy to be connected to or disconnected from the test vehicle. An example of the prior-art automatic vehicle driving system is disclosed in Transactions No. 862, October, 1986 by JAPANESE AUTOMOBILE TECHNOLOGY ASSOCIATION.
This prior-art driving system will be described hereinbelow with reference to FIGS. 1(a) to (d). The system comprises an actuator composed of plural double acting air cylinders 46 for actuating an accel pedal 42, a brake pedal 43, a clutch pedal 44 and a shift lever 45 in accordance with each command stroke; an actuator controller composed of an electromagnetic unit 48, a plurality of electromagnetic valve actuating circuits 49, and a plurality of 8-bit one-chip microcomputer (i.e. microprocessor .mu.p) 50; and a main controller composed of a general purpose 16-bit personal computer 55.
Various test conditions such as engine speed N.sub.e, a vehicle speed V, current air cylinder positions of the air cylinders 46 (each detected by a potentiometer 47), etc. are inputted to the personal computer 55 through a keyboard as external commands. Further, as shown in FIG. 1(b), it is possible to select operations of "TEACHING (automatic measurement)", "AUTO TRAVEL", "MANUAL TRAVEL", and "END" through the keyboard. A CPU within the personal computer 55 executes each selected operation.
The TEACHING operation can be classified into two teaching operations of transmission gear change position teaching and pedal position teaching. In the transmission gear change position teaching, whenever the operator manually operates the transmission shift lever 45 for shift gear change, each shift gear position is stored in a memory unit within the computer 55 as teaching data. In the pedal position teaching, whenever the three pedals 42 to 44 are depressed automatically on the basis of a program, a play (free travel) of the accel pedal 42, an effective position of the brake pedal 43, an engage position of the clutch pedal 44, etc. are stored as teaching data.
When "AUTO TRAVEL" is selected, an actual vehicle speed detected by the dynamometer is compared with a command vehicle speed stored in the memory, and either of the accel pedal 42 and the brake pedal 43 is depressed to match the actual vehicle speed with the command vehicle speed by operating each air cylinder 46 at an appropriate timing. The command position L.sub.s and the current position L.sub.i of each air cylinder 46 is transmitted to each microcomputer 50, respectively, to calculate a difference .DELTA.L between the command position L.sub.s and the current position L.sub.i and determines a valve open duration according to the difference .DELTA.L with reference to table data, so that the current position L.sub.i coincides with the command position L.sub.s in each air cylinder 46. In this operation, the air cylinder 46 is driven by actuating two electromagnetic valves A and Aa or B and Ba, respectively as shown in FIG. 1(c), on the basis of a positive or negative sign attached to the calculated position difference.
For instance, in FIG. 1(c), when the accel pedal 42 is required to be depressed to shift the current position L.sub.i to be command position L.sub.s of the piston 46A of the air cylinder 46, two electromagnetic valves A and Aa are selected and opened for a time period according to the calculated position difference with the valves B and Ba kept closed.
Further, each electromagnetic valve A, Aa, B or Ba is composed of two parallel arranged electromagnetic valves connected between a pressurized air inlet port 58A into which pressurized air of 5 kgf/cm.sup.2 is introduced and an outlet port 58B exposed to atmospheric pressure, a shown in FIG. 1(d). The reason why two cylinders are arranged in parallel is that the piston can be moved at higher speed when the number of the electromagnetic valves increases. For the same reason as described above, three parallel-arranged electromagnetic valves are connected in parallel to the air cylinder for the clutch pedal in order to further increase the gear shift time.
In FIG. 1(d), when the valves A and Aa are opened, since pressurized air (5 kgf/cm.sup.2) is introduced into the right chamber 46B via the valves A and further air is exposed from the left chamber 46C to the atmosphere via the valves Aa, the piston 46A moves leftward to the command position L.sub.s. On the basis of the movement of the piston 46A, the accel pedal 42 is further depressed via a wire 56 and a link mechanism 57 both shown in FIG. 1(c).
As described above, each pedal 42 to 44 and the shift lever 45 are actuated automatically in accordance with the position control of the air cylinders 46.
In the prior-art automatic vehicle driving system as described above, however, since the actual vehicle speed is compared with the command vehicle speed and the positions of the air cylinders 46 are controlled so that the actual vehicle speed becomes equal to the command vehicle speed, it is necessary to determine optimum control gains for each test vehicle. Here, the control gain implies a constant required to convert a difference between the actual vehicle speed and the command vehicle speed into each air cylinder movement stroke.
Therefore, whenever the test vehicle changes, since the optimum control gain (conversion constant) also changes, there exists a problem in that the control gain must be set according to each test vehicle. The above-mentioned problem also arises whenever the load conditions of the chassis dynamometer change. In other words, since the optimum control gains are different according to command vehicle speed data stored in the memory so as to be suitable for each test vehicle, there exists a problem in that the control gain setting work is troublesome and therefore it takes much time to adjust the control gains.